[LV] [PATCH] Permit variadic syscalls

[Maciej W. Rozycki]

 A few Linux syscalls have variadic arguments.  These include open(2) that 
accepts either two or three arguments and reboot(2) that takes either 
three or four.

 Make the debug argument-count verification code accept variadic syscalls 
with a dedicated count check as special cases.

Signed-off-by: Maciej W. Rozycki <macro at linux-mips.org>
---
Jan-Benedict,

 I gather you have not yet applied the original open(2) patch this one 
builds upon:

Message-ID: <alpine.LFD.1.10.0905172337160.14684 at ftp.linux-mips.org>
Date: Mon, 18 May 2009 00:57:01 +0100 (BST)
From: Maciej W. Rozycki <macro at linux-mips.org>
To: Jan-Benedict Glaw <jbglaw at lug-owl.de>
Cc: linux-vax at pergamentum.com
Subject: [PATCH] Permit 2- and 3-argument calls to open(2)

 Please replace it with the following one.  Note that glibc (up to current 
GIT HEAD) is particularly keen on calling reboot(2) with three arguments 
only.  I found this one with init(8).  There might be more such syscalls 
still undiscovered.

 Please apply.

  Maciej

patch-mips-2.6.25-20080422-vax-scall-varargs-0
Index: linux-mips-2.6.18-20060920-cougar/arch/vax/kernel/syscall.c
===================================================================
--- linux-mips-2.6.18-20060920-cougar.orig/arch/vax/kernel/syscall.c
+++ linux-mips-2.6.18-20060920-cougar/arch/vax/kernel/syscall.c
@@ -58,7 +58,7 @@ extern asmlinkage long sys_rt_sigaction(
 
 static struct {
 	unsigned long	*sc_func;
-	unsigned int	nr_args;
+	int		nr_args;
 } syscall[] = {
 #define SC(num, func, args)					\
 	[num] = {						\
@@ -69,7 +69,7 @@ static struct {
 	SC (__NR_fork,		sys_fork,		0),
 	SC (__NR_read,		sys_read,		3),
 	SC (__NR_write,		sys_write,		3),
-	SC (__NR_open,		sys_open,		3),
+	SC (__NR_open,		sys_open,		-1),
 	SC (__NR_close,		sys_close,		1),
 	SC (__NR_waitpid,	sys_waitpid,		3),
 	SC (__NR_creat,		sys_creat,		2),
@@ -140,7 +140,7 @@ static struct {
 	SC (__NR_readlink,	sys_readlink,		3),
 	SC (__NR_uselib,	sys_uselib,		1),
 	SC (__NR_swapon,	sys_swapon,		2),
-	SC (__NR_reboot,	sys_reboot,		4),
+	SC (__NR_reboot,	sys_reboot,		-1),
 	SC (__NR_mmap,		sys_mmap,		6),
 	SC (__NR_munmap,	sys_munmap,		2),
 	SC (__NR_truncate,	sys_truncate,		2),
@@ -287,7 +287,8 @@ void syscall_handler(struct pt_regs *reg
 {
 	unsigned int sc_number;
 	unsigned int *user_ap;
-	unsigned int nr_args;
+	int sc_args;
+	int nr_args;
 
 	sc_number = *(unsigned int *)(excep_info);
 
@@ -347,17 +348,33 @@ void syscall_handler(struct pt_regs *reg
 	/*
 	 * Check number of syscall arguments
 	 */
-	if (unlikely (syscall[sc_number].nr_args != nr_args)) {
-		printk (KERN_DEBUG "%s(%d): stack mismatch (should=%d, caller=%d) on syscall %d\n",
+	sc_args = syscall[sc_number].nr_args;
+	if (unlikely(sc_args != nr_args))
+		switch (sc_args) {
+		case -1:
+			/* Variadic syscalls:  */
+
+			/* open(2) takes two or three args.  */
+			if (sc_number == __NR_open && !((nr_args - 2) & ~1))
+				break;
+
+			/* reboot(2) takes three or four args.  */
+			if (sc_number == __NR_reboot && !((nr_args - 3) & ~1))
+				break;
+
+		/* Fall through.  */
+		default:
+			printk(KERN_DEBUG "%s(%d): stack mismatch "
+				"(should=%d, caller=%d) on syscall %d\n",
 				current->comm, current->pid,
-				syscall[sc_number].nr_args, nr_args, sc_number);
-		printk (KERN_DEBUG "Please report to "
+				sc_args, nr_args, sc_number);
+			printk(KERN_DEBUG "Please report to "
 				"<linux-vax at pergamentum.com>.\n");
 #ifdef CONFIG_DEBUG_VAX_CHECK_CHMx_ARGS_ABORT
-		regs->r0 = -EFAULT;
-		return;
+			regs->r0 = -EFAULT;
+			return;
 #endif /* CONFIG_DEBUG_VAX_CHECK_CHMx_ARGS_ABORT */
-	}
+		}
 #endif /* CONFIG_DEBUG_VAX_CHECK_CHMx_ARGS */
 
 	/*
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